(1) Field of the Invention
The present invention relates to a solid-state imaging device and a camera that include a semiconductor substrate having plural light-receiving units, and lenses and color filters formed inside a layer, corresponding to the respective light-receiving units.
(2) Description of the Related Art
In recent years, with achievements of miniaturizing chip size and increasing the number of pixels of a solid-state imaging device, developments to achieve the miniaturization and high-performance of a digital camera, a digital movie camera, a camera-equipped cell phone and the like are proceeding.
A conventional solid-state imaging device has light-receiving units having respective micro-lenses in order to increase sensitivity, while the chip size is miniaturized and the number of pixels is increased in the solid-state imaging device.
While the microlenses are formed only on a top surface part of a chip in the conventional technology, it is getting difficult to obtain sufficient light-collecting efficiency only using the microlenses formed on the top surface part as the pixel size is further miniaturized. Accordingly, there is provided a solid-state imaging device in which in-layer lenses are formed between the microlens formed on the top surface part and the light-receiving units so that a higher light-collecting efficiency is achieved.
Also, along with the miniaturization of a camera, the development has been made to achieve short eye relief in a digital still camera, a camera-equipped cell phone and the like. Here, an exit pupil is a virtual image of a lens (or an aperture) seen from a light-receiving face side, and an eye relief is a distance from the light-receiving face to a virtual image point of the lens.
FIG. 1 is a cross-sectional drawing showing a camera part of a cell phone and the like for explaining an eye relief. In the drawing, a lens 80 is attached to a frame 81 of the cell phone which includes a Charge Coupled Device (CCD) image sensor 82 as a solid-state image device. An eye relief D is a distance between a virtual image point of the lens 80 and the CCD image sensor 82. By shortening the eye relief, light is incident vertically on a center part of the light-receiving face, while the light is incident not vertically but only diagonally on a peripheral part of the light-receiving face.
FIG. 2A and FIG. 2B are cross-sectional drawings, each of which shows a positional relationship between the light-receiving units and the microlenses in the conventional solid-state imaging device as disclosed, for example, in Japanese Patent Publication No. 11-40787. FIG. 2A shows a center part of an imaging area in which the light-receiving units are arranged in a two-dimensional array. FIG. 2B shows a peripheral part of the imaging area. Here, arrows in the drawings indicate incident light. The solid-state imaging device includes: a semiconductor substrate 101; light-receiving units 102 formed in the semiconductor substrate 101; transfer electrode units 103, each of which made up of a transfer electrode and a light-shielding film; in-layer convex lenses 104; a planarizing film 105 for planarizing the surfaces of the light-receiving units 102, the transfer electrode units 103 and the in-layer convex lenses 104; color filters 106R, 106G and 106B respectively for colors of red, green and blue; a planarizing film 107 under the microlenses 108; and microlenses 108. As the arrows indicate, the incident light is incident nearly vertical to the center part of the imaging area, while it is incident diagonally to the peripheral part as the eye relief is shorter.
FIG. 3 is a drawing showing a method of forming conventional in-layer convex lenses. As shown in FIG. 3(a), a transparent material 151 (e.g. plasma nitride film) is deposited using a Plasma Chemical Vapor Deposition (CVD) method. Next, as shown in FIG. 3(b), a resist is patterned on the transparent material 151 via a mask, and convex patterns 152 are formed on the resist by further performing reflow processing. Lastly, as shown in FIG. 3(c), the transparent material 151 deposited on the convex patterns 152 is etched so as to copy the shape of the convex patterns as masks, and the intra-convex lenses as shown in FIG. 3(d) are formed.
However, according to the conventional technology, the microlenses formed on the top surface part are formed in a same shape and made of a same material despite the color arrangements. The same thing applies to among the in-layer lenses. Therefore, different light-collecting effects are obtained depending on the wavelengths, causing a problem of worsening the sensitivity and color reproducibility.
Further, according to the conventional technology, there is a problem that color shading is generated in the peripheral part of the imaging area as shortening the eye relief. In other words, there is a problem that the peripheral part of the image is colored because of the collapse of the white balance.
It is because refractive indexes of the in-layer lenses are different depending on colors as well as those of the microlenses, which mean wavelengths, and the differences of the refractive indexes cause differences of light-collecting state on the light-receiving faces of respective color arrays. In the case where incident light spreads without being collected sufficiently on the light-receiving faces, the incident light is likely to be incident out of the light-receiving units so that the sensitivity is lowered. In the case where the light-collecting states on the light-receiving faces are different for respective color arrays, the color shading is generated because the differences of sensitivities among colors are generated.